try making them smaller...I usually use the dimensions 400 x 150, or 350 x 100...also, try to match the colors and style of your render to the bg...for instance....here are some steps i would take to fix the first 1...
1) restart it...lol...only way to fix it withut it lookin bad...
2) place your render into the blank doc (400x150)
3) fill the background with black
4) use some white brushes to make a decent background
5) duplicate the render and use smudging, layer settings etc. to add to the overall look of the sig.
6) once u have done that, add some text to a open part of the sig, snce its dark use white text, and a font that matches the sig style and render.
7) since this is a beginner sig just lower the opacity or change the layer setting of the text until it looks good.

add a border if u want
thats it....its a very brginner tut i just pulled out of my *** lol...and it prob wont end up being amazing...and i rele didnt get into details...but its a good start